A plethora of applications exist for effecting electrical contact between two conductors. One significant application is effecting interconnection between the leads of an integrated circuit device and conductive pads or terminals on a printed circuit board. Numerous considerations bear upon the structure employed to interconnect the IC and the printed circuit board, including both electrical and mechanical considerations.
One important mechanical consideration is the degree and type of wiping action that is provided by the interconnect system. A wiping action between the contact itself and the lead of an IC, for example, functions to effect maximization of effective contact in view of oxide build-up which can occur. In effect, the wiping action enables a good interface to be accomplished between the contact and the lead of the IC. Thus, it is desirable for the interconnect system to provide a wiping action between the contact and the device lead. Further, and under some circumstances, it is also desirable for the interconnect system to provide a wiping action between the contact and the printed circuit board terminal.
In addition to the above, it is desirable that the interconnect system accommodate non-planer device leads. In some interconnect systems, device leads that are non-planer may be bent or otherwise stressed during the engagement of the device leads with the interconnect system. To overcome this difficulty, elastomeric elements may be used to support the contacts to allow deflection of the contacts. Prior art interconnect system that use elastomer elements are described in U.S. Pat. No. 4,445,735, issued on May 1, 1984 to Bonnefoy; U.S. Pat. No. 4,509,099, issued on Apr. 2, 1985 to Takamatsu et al.; U.S. Pat. No. 4,593,961, issued on Jun. 10, 1986 to Cosmo; and U.S. Pat. No. 4,793,814, issued on Dec. 27, 1988 to Zifcak et al.
A potential limitation of using elastomeric elements within an interconnection system is that the contact may not maintain a good electrical and mechanical connection between the contacts and the pads or terminals of a printed circuit board, and thus may limit the wiping action provided thereby. For example, the apparatus disclosed in U.S. Pat. No. 4,793,814, issued to Zifcak et al. may not provide a good electrical or mechanical connection between the contact and the pads or terminals of the printed circuit board upon initial engagement of the contacts and the contact pads 34. That is, and with reference to FIGS. 3-4 of Zifcak et al., the lower ends of the contacts 22 would, upon initial engagement by the contact pads 34, provide an upward force on the elastomeric support member 13. However, the elastomeric support member 13 is not prevented from deforming in an upward direction until the board surface 15 comes into engagement therewith. Thus the lower ends of the contacts may loose contact or otherwise may be limited in the amount of force provided between the contact and the contact pads 36. Thus, during at least this portion of the contact actuation cycle, the wiping action provided between the contacts and the contact pads may be limited.
Another potential limitation of using elastomeric elements within an interconnection system may be caused by the relative temperature expansion coefficients of the elastomeric element relative to the corresponding printed circuit board and/or device package. That is, for some prior art interconnection systems, the difference between the temperature expansion coefficients of the elastomeric element and printed circuit board and/or device package may cause misalignment between the contacts embedded therein and the corresponding device and/or printed circuit board terminals. This may limit the contact pitch provided by such systems.
Another important consideration is the expected reliability of the interconnect system. In one application, interconnect systems are used as test sockets for testing integrated circuits. In such an application, each fabricated integrated circuit is inserted into the interconnect system, tested, and then removed. As indicated above, it is desirable for a wiping action to occur between the integrated circuit leads and corresponding contacts of the interconnect system. However, it is known that the wiping-action may produce solder-buildup at or near the contacting portions of the contact. Thus, it is desirable for the interconnect system to be design to minimize solder-buildup, and to minimize the effects of solder-buildup on the overall reliability of the interconnect system.
It is also recognized that the contacts and elastomeric element themselves may become worn after extended use. In view thereof, it is desirable for the components, and in particular the contacts and the elastomer elements, to be replaceable such that worn components can be easily removed and replaced.
Another important consideration is the ease of manufacture of the interconnect system. In particular, the assembly of the constituent components of the interconnect system should be made as simple as possible. A simple assembly process may reduce the manufacturing cost of the interconnect system, as well as the maintenance thereof.